Hydrodynamic bearing device, and spindle motor and information device using the same

Abstract

A hydrodynamic bearing device has high reliability and is suitable for miniaturization through superior heat resistance and by utilizing a dynamic pressure-generating liquid with little loss due to evaporation. The hydrodynamic bearing device has at least one of a shaft structure and a sleeve having a dynamic pressure-generating mechanism. The dynamic pressure-generating liquid present in a gap between the shaft structure and the sleeve has a main component that is ionic liquid.

1. A hydrodynamic bearing device, comprising at least one of a shaft structure and a sleeve having a dynamic pressure-generating mechanism, and a dynamic pressure-generating liquid present in a gap between the shaft structure and the sleeve;
 wherein the main component of the dynamic pressure-generating liquid is at least one selected from the group consisting of 
 ionic liquids having viscosity index of 150 or more; 
 ionic liquids having surface tension of 35 mN/m or more at 20° C.; and 
 ionic liquids having mean coefficient of volume expansion between 0° C. and 80° C. of 7.0×10 −4 K −1  or less; and 
 each of the ionic liquids are at least one selected from the group consisting of imidazolium salts, pyridinium salts, ammonium salts and phosphonium salts as positive ions, and at least one selected from the group consisting of halides, nitrates, sulfur containing groups, fatty acids, cyano groups and perfluoro groups as negative ions. 
 
     
     
       2. A hydrodynamic bearing device, comprising at least one of a shaft structure and a sleeve having a dynamic pressure-generating mechanism, and a dynamic pressure-generating liquid present in a gap between the shaft structure and the sleeve;
 wherein the main component of the dynamic pressure-generating liquid is at least one selected from the group consisting of 
 ionic liquids having viscosity index of 150 or more, 
 ionic liquids having surface tension of 35 mN/m or more at 20° C.; and 
 ionic liquids having mean coefficient of volume expansion between 0° C. and 80° C. of 7.0×10 −4 K −1  or less; and 
 each of the ionic liquids are at least one compound represented by 
 
       
         
           
           
               
               
           
         
         wherein, R represents a hydrogen atom or any C1-C14 alkyl, and when there is more than one R in the molecular formula, each R has an identical structure, or the structures of some or all R are different, and wherein X is at least one selected from the group consisting of inorganic ions and organic ions. 
       
     
     
       3. The device as recited in  claim 2 , wherein R is a C1-C14 alkyl, said C1-C14 alkyl being one of methyl, ethyl, propyl, iso-butyl, n-butyl, pentyl, tetradecyl alkyls, wherein said one inorganic ions is at least one of Cl, Br, BF 4 , PF 6 , NO 3  and halide, and wherein said organic ions is at least one of HSCN, CF 3 SO 3 , CF 3 (CF2) 3 SO 3 , CF 3 (CF 2 ) 7 SO 3 , (CF 3 SO 2 ) 2 N, (C 2 F 5 SO 2 ) 2 N, p-CH 3 C 6 H 4 SO 2 , CH 3 SO 3 , C 8 H 17 OSO 3 , CH 3 OSO 3 , CH 3 O(C 2 H 4 O) 2 SO 3 , [(CH 3 ) 3 CCH 2 CH(CH 3 )CH 2 ] 2 P(O)O, CH 3 (CH 2 ) 8 CO 2 , N(CN) 2 ).